Although it has not been clarified yet how nasal polyp is formed, it was formerly thought that inflammation by infection participated in its origin because it is an inflammatory lesion which is perceived being associated with chronic sinusitis. On the other hand, when nasal polyp is histologically observed, many of it is associated with eosinophilic infiltration and, therefore, its origin has been also presumed to be participation of eosinophilic inflammation such as bronchial asthma and allergic rhinitis.
Nasal polyp induces not only nasal obstruction and heavy feeling of the head among the symptoms of chronic sinusitis but also makes the sinusitis severe due to ventilatory disorder of paranasal sinus and disorder of lower respiratory tract due to postnasal drip.
Accordingly, although the treatment of chronic sinusitis accompanied by nasal polyp is an surgical therapy, recurrence is noted within two to three years in the case where asthma is complicated therewith or in the case where local eosinophilic infiltration is severe.
When patients suffering from allergic rhinitis represented by hay fever or from allergic bronchial asthma are exposed to antigen, chemical mediators such as prostaglandin (PG)D2, PGE2, histamine and leukotriene (LT)C4, LTD4 and LTE4 are excessively produced and released from mast cells and then inflammatory cells represented by eosinophils are locally accumulated. When the accumulated eosinophils are activated, they are thought to release tissue-injuring proteins such as major basic protein (MBP) and eosinophilic cationic protein (ECP) and they make the inflammation more serious.
Prostaglandin D2 (PGD2) has been known to be involved in diseases such as chronic sinusitis (nasal polyp), allergic rhinitis, bronchial asthma (particularly allergic bronchial asthma) and allergic dermatitis (e.g. Non-Patent Documents 1 and 2). On the other hand, amount of PGE2, LTC4, LTD4 and LTE4 and infiltration numbers of eosinophils have been used as indexes for severity in those diseases. However, to date diagnosis on severity of those diseases and their prediction recurrence by evaluating the expression of hematopoietic prostaglandin D synthase (H-PGDS) protein in the inflammatory sites has been reported.
Administration of steroids (glucocorticoids) shows a significant effect for the treatment of those diseases but, in view of their side effects, chronic administration is limited. Although administration of nonsteroidal anti-inflammatory drugs, antiallergic agents, antihistaminic agents or anti-leukotriene agents is presently in practice, variation on their effect among individuals is large.    Non-Patent Document 1: Allergy, Vol. 54, No. 3/4, Page 384    Non-Patent Document 2: Allergy, Vol. 52, No. 8/9, Page 759